LibSass fails to parse unary / after comma

[nex3]

The expression (1, / 2) should produce the output 1, /2. LibSass fails to parse it:

Error: Invalid CSS after "...ter-comma:  (1,": expected expression (e.g. 1px, bold), was "/ 2);"
        on line 11 of spec/parser/operations/binary-and-unary/input.scss
>>   slash-after-comma:  (1, / 2);
   --------------------------^

I'm adding a spec for this in sass/sass-spec#1110.

[mgreter]

Should be fixed by #2388